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Encapsulated materialsRelated Patent Categories: Stock Material Or Miscellaneous Articles, Coated Or Structually Defined Flake, Particle, Cell, Strand, Strand Portion, Rod, Filament, Macroscopic Fiber Or Mass Thereof, Particulate Matter (e.g., Sphere, Flake, Etc.), CoatedEncapsulated materials description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070092726, Encapsulated materials. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a process for forming capsules. An encapsulation process generally comprises the following steps: [0002] (a) forming a dispersion of a core material in a continuous phase containing a wall forming material; [0003] (b) depositing the wall material upon the surface of a core material to form capsules; [0004] (c) hardening of the capsules; and [0005] (d) recovering the capsules. [0006] The continuous phase in step (a) is normally a solution of the wall material. If the core is a liquid, it is dispersed or emulsified in said solution; if, however, the core is a solid, it is usually pre-ground to the desired size and then dispersed within the solution. Step (b) generally involves changing the conditions of the solution in such a way as to cause phase separation of the wall material from the continuous phase. Normally, the wall material is caused to phase separate from the continuous phase, whereby at least part of the wall material forms a coherent film around the particles or droplets of the core phase. This liquid, amorphous or gelatinous wall phase is subsequently hardened (step (c)), before recovery of the capsules. Capsule recovery is effected by filtering, centrifuging and the like, optionally followed by drying in case the capsules are to be recovered as a dry powder. As is known to the skilled person, capsules can have a variety of shapes, depending a.o. on the shape of the core material and on the regularity of the wall material. As long as a minimum wall material thickness is present such that the core material is sufficiently encapsulated, it is usually not necessary that wall material thickness is perfectly uniform throughout a capsule. It is also possible that a capsule is in fact a regularly or irregularly shaped agglomerate of several smaller whole or partial capsules. In some instances, the dried product is a caked powder and must be reduced to a free flowing powder by a gentle grinding operation, e.g., sieving. [0007] A well-known and often used wall forming material is melamine-formaldehyde resin. The thus formed melamine-formaldehyde capsules are e.g. used to encapsulate aromatizing and flavoring agents and vitamins. [0008] An important drawback of melamine-formaldehyde as wall forming material is that a slight formaldehyde emission is still observed. During the production of the resin and the encapsulated product, but also from the capsule itself, vapours are released that may be irritating and even toxic. Residues of the original raw materials always remain behind, also after polymerisation. In cured condition, formaldehyde slowly diffuses from the product. This formaldehyde emission is not desirable, definitely not in a confined area. In such areas formaldehyde is inhaled and contacts the eyes, mouth and other parts of the body. Formaldehyde gas causes irritation of the eyes and respiratory tract and is toxic. Moreover, when the capsules are further degraded, e.g. by hydrolysis, after use or during de-encapsulation, an even larger portion of the original formaldehyde content of the original wall material, potentially even all of it, is released to the direct environment of the capsule. A disadvantage of the capsules based on melamine-formaldehyde capsules therefore is the formation of the injurious formaldehyde. [0009] An aim of the present invention is to provide a process for forming capsules, which do not release free formaldehyde. This aim is achieved in a process for forming capsules comprising the steps of: [0010] (1) forming a solution of an amino compound (I) in a solvent; [0011] (2) forming a dispersion of a core material in the solution; [0012] (3) depositing the amino compound as a resin upon the surface of the core material to form capsules; and [0013] (4) optionally hardening and/or recovering the capsules, whereby steps (1) and (2) are executed in either order or simultaneously, and wherein amino compound (I) has the following formula [0014] where: [0015] X is O or NR.sub.5; [0016] EWG is an electron-withdrawing group; [0017] R.sub.1, R.sub.2, R.sub.3, R.sub.5 are equal to an H, alkyl, cycloalkyl, aryl of heterocyclic group; and [0018] R.sub.1, R.sub.2, and R.sub.5 or R.sub.1, R.sub.2, and R.sub.3 may together form a heterocyclic group. [0019] Electron-withdrawing groups (EWG) are as such known to the skilled person. Examples of EWG are acid-, ester-, cyano-, di-alkylacetal-, aldehyde-, substituted phenyl-, or trihalomethyl groups. Hydrogen is not an EWG. [0020] An amino compound is defined herein as a compound having at least one NH or NH.sub.2 group, attached to an electron-attracting atom or to an atom that is connected to electron-attracting atom or group. The number of amino groups per amino compound generally is at most 3. Examples of electron-attracting atoms are oxygen, nitrogen and sulphur. Suitable amino compounds are for example triazines, guanidine, urea, and mixtures of these compounds. Aminoplasts such as melamine-formaldehyde, urea-formaldehyde and melamine-urea-formaldehyde may also be employed as amino compound. Preferably, urea or triazines such as melamine, melam, melem, ammeline, ammelide and ureidomelamine are used. In particular melamine is used. [0021] Steps (1) and (2) can be carried out in the reversed sequence or in parallel, such that the solution and the dispersion both in the solvent are mixed together. Thus, the description of step (2) as given above should be interpreted to encompass the meaning that a dispersion of the core material is formed in the solvent rather than in the solution, this being the case if step (2) is carried out prior to or simultaneously with step (1). [0022] The first step in the process of the invention is forming a solution of a compound according to formula (I). A compound according to formula (I) is preferably prepared by reacting an amino compound with an aldehyde according to formula (II) or with an aldehyde derivative. An aldehyde derivate herein means an aldehyde hydrate according to formula (III) or an alkanol hemiacetal according to formula (IV): [0023] Examples of aldehydes according to formula (II) are glyoxilic acid, dimethoxyacetaldehyde, diethoxyacetaldehyde, ethylglyoxylate, butylglyoxylate, and o-phtalaldehyde. Examples of aldehyde hydrates according to formula (Ill) are glyoxylic acid hydrate, chloral hydrate, and glyoxal hydrate. In formula (IV), R.sub.6 stands for a C.sub.1-C.sub.12 alkyl group, aryl group, aralkyl group or a cycloalkyl group. Examples of alkanol hemiacetals accoding to formula (IV) are methylglyoxylate methanol hemiacetal and ethylglyoxylate ethanol hemiacetal. [0024] The process for the preparation of the compound according to formula (I) will usually occur spontaneously once the amino compound and the compound according to formula (II), (III) or (IV) have been brought into contact with each other. The temperature in the present process can thus vary within wide limits, and preferably lies between 10.degree. C. and 90.degree. C. Most preferably the process is carried out at between 40.degree. C. and 80.degree. C. The process for preparing the amino compound according to formula (I) follows the general rule that it proceeds more quickly if the temperature is raised. An additional control mechanism to influence the reaction rate is the pH, because the addition of either an acid or a base has a catalytic effect. The pH may be adjusted to a value lying preferably between 2 and 10. Thus, the skilled person can easily--by adjusting temperature and pH--find the circumstances under which a desirable reaction rate is achieved. [0025] The pressure in the present process preferably is between 0.005 MPa and 1.0 MPa, preferably between 0.02 MPa and 0.1 MPa. The process is preferably carried out in a solvent such as for example water or a mixture of water and alkanol. Water is the preferred solvent. Examples of alkanols are methanol, ethanol, propanol, butanol, pentanol. [0026] Starting from the fact that the number of amino groups per amino compound generally is at most 3, the molar ratio beween amino group and aldehyde or aldehyde derivative is poreferably between 3 and 1. With more than 3 amino groups per aldehyde or aldehyde derivative, the molecular weight of the resin will be limited, while a ratio below 1 is limiting for crosslinking of the resin and leaves free aldehyde or aldehyde derivative in the solvent. [0027] In a preferred embodiment of the process according to the invention, in step (1) a solution of a compound (V) from an amino compound/alkanol hemiacetal mixture in a solvent is formed, wherein compound (V) falls within the scope of formula (I) and is an amino compound according to the following formula: [0028] where: [0029] X is equal to O or NR.sub.5; [0030] R.sub.4 is equal to a C.sub.1-C.sub.12 alkyl group, aryl group, aralkyl group or cycloalkyl group; [0031] R.sub.1, R.sub.2, R.sub.3 R.sub.5 are equal to an H, alkyl, cycloalkyl, aryl of heterocyclic group; and [0032] R.sub.1, R.sub.2, and R.sub.5 or R.sub.1, R.sub.2, and R.sub.3 may together form a heterocyclic group. [0033] Preferably R.sub.4 is a C.sub.1-C.sub.12 alkyl group. Examples hereof are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl etc. R.sub.4 is in particular a methyl group or an ethyl group. [0034] A compound according to formula (V) can be prepared by reacting an amino compound and an alkanol hemiacetal of the following general formula (VI): where R.sub.4 and R.sub.6 are a C.sub.1-C.sub.12 alkyl group, aryl group, aralkyl group or cycloalkyl group, in which process an alkanol is released. [0035] Preferably R.sub.4 and R.sub.6 are C.sub.1-C.sub.12 alkyl groups. Examples hereof are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl etc. R.sub.4 and R.sub.6 are in particular a methyl group or an ethyl group. [0036] Examples of alkanol hemiacetals of formula (Vl) are: methylglyoxylate methanol hemiacetal (GMHA.RTM., DSM Fine Chemicals, Linz); ethylglyoxylate ethanol hemiacetal (GEHA.RTM., DSM Fine Chemicals, Linz); ethylglyoxylate methanol hemiacetal; butylglyoxylate butanol hemiacetal; butylglyoxylate methanol hemiacetal; butylglyoxylate ethanol hemiacetal; isopropylglyoxylate isopropanol hemiacetal; propylglyoxylate propanol hemiacetal; cyclohexylglyoxylate methanol hemiacetal and 2-ethylhexylglyoxylate methanol hemiacetal. It is also possible to use ethyl or butyl glyoxylate in stead of the hemiacetal. [0037] The second step in the process of the invention is forming a dispersion of a core material in the solution. If the core is a first liquid, the material to be encapsulated can be this first liquid. The core material can also be a solid or a second liquid which is dissolved or dispersed in said first liquid. Said first liquid preferably is a high boiling hydrophobic liquid such as an oil. Suitable oils, are in particular vegetable and animal oils, fatty esters and waxes, partly hydrogenated terphenyls, chlorinated paraffins, alkylated biphenyls, alkyl naphthalenes, diaryl methane derivatives, dibenzyl benzene derivatives, alkanes, cycloalkanes and esters, such as phthalates, adipates, trimellitates and phosphates, and silicone oils. [0038] To stabilize the dispersion a surfactant can be added. Suitable surfactants can be found among ionic and non-ionic surfactants. The surfactant preferably is an anionic or non-ionic surfactant. It is not always necessary to use such a surfactant, since many of the compounds according to formula (VI) spontaneously form small amounts of anionic groups through hydrolysis which can act as a surfactant. [0039] The third step in the process of the invention is depositing the compound as a resin upon the surface of the core material to form capsules. Step (3) generally involves changing the conditions in such a way as to cause phase separation of the wall material from the continuous wall solution phase. Normally, the wall forming material is caused to phase separate from the continuous phase, at least partially as a coherent film around the particles or droplets of the core phase in a process which preferably lasts between several minutes and hours. Phase separation can be introduced by an increase or decrease of the temperature. A decrease of temperature may cause phase separation due to a decreased solubility, while an increase of the temperature may cause the resin to pass over its cloud point. [0040] An alternative way of phase separation is to increase the molecular weight of the resin. This is effected by prolonged polymerization of the compound according to formula (I) or (V) in the solvent. This will decrease the solubility of the resin in the solvent. Continue reading about Encapsulated materials... 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